(58e) Wax Deposition and Control in North Sea Oil and Gas Production Systems

An overview of experiences with production of waxy petroleum fluids on the Norwegian continental shelf (NCS) is provided.  

Although wax deposition is normally avoided by good thermal design (insulation, heating) and operational practice, there are several examples of production and transport systems where wax deposition has been experienced.

A long condensate export pipeline which started to experience severe wax deposition, and corresponding increase of pressure drop, when a waxy condensate was introduced, is given special attention.  Wax deposit thickness measurements by a pressure pulse technique and tracer injection has provided useful information about the pipeline status, allowing controlled operation of the line.  Attempts have been made to clean the line by chemical treatment, unsuccessfully.  A new, highly sophisticated wax removal pig for thick deposits has recently been qualified by Statoil in order to clean the pipeline.  

Other examples of wax deposition and wax control in export pipelines, multiphase flow lines and risers, are described.  Special design and operational issues related to wax pigging of complex multi-node export pipeline systems, pigging of multiphase gas dominated flow lines, production of low temperature reservoirs and production of high pour point fluids are mentioned.   Examples of ongoing activities to improve the prediction of wax pigging frequency will be shown.

An integrated cold flow concept for long distance multiphase transport of waxy oils, based on technology patented by Statoil, is described. This may be a candidate for long tie-backs of remote reservoirs to shore or a central hub.